package main

func fibonacci(n int) (res int) {
	if n == 0 {
		res = 1
	} else if n == 1 {
		res = 1
	} else {
		res = fibonacci(n-1) + fibonacci(n-2)
	}
	return
}

func even(n int) bool {
	if n == 0 {
		return true
	}
	return odd(revSign(n) - 1)
}

func odd (n int) bool {
	if n == 0 {
		return false
	}
	return even(revSign(n) - 1)
}

func revSign(v int) int {
	if v < 0 {
		return -v
	}
	return v
}
